Photographic processes using silver halide have been widely used in the past due to their excellent photographic properties such as sensitivity or control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques capable of easily and quickly providing images have been developed by changing the conventional wet process using a developing solution into a dry development process such as a process using heat, etc.
Heat developable light-sensitive materials are thus well known in this field. Heat developable light-sensitive materials and processes therefor have been described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553-555 (published by Corona Co., 1979), Eizo Joho (The Image Information), page 40 (April, 1978), Nebletts Handbook of Photography and Reprography, 7th Ed., pages 32-33 (Van Nostrand Reinhold Company), U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777 and Research Disclosure, No. 17029, pages 9-15 (June, 1978).
Many different processes for obtaining color image have been proposed. With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, pages 31-32 (September 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Also, processes and materials for forming a positive color image by a light-sensitive silver dye bleach process are described, for example, in Research Disclosure, No. 14433, pages 30-32 (April, 1976), ibid., No. 15227, pages 14-15 (December, 1976) and U.S. Pat. No. 4,235,957, etc.
Further, processes for forming images upon heat development utilizing compounds having a dye moiety which are capable of releasing a mobile dye in correspondence or counter-correspondence to the reduction reaction of silver halide to silver under high temperature conditions have been described, for example, in European Patent Application (OPI) Nos. 76,492 and 79,056, Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), etc.
With these heat developable light-sensitive materials development is conducted by heating using a base as a development accelerator in most cases. However, light-sensitive materials once heated at high temperature take a substantial time to decrease in temperature, resulting in overdevelopment or deterioration of image quality. Further, it is possible for development to occur beyond the desired level depending on subtle variations in conditions such as the ambient temperature, the temperature of heating, the moisture content of the light-sensitive material, the time of heating, etc., even when the same pattern of heating is employed.
In order to eliminate such a phenomenon, it has been proposed to use acid polymers for neutralization as described in Research Disclosure, Vol. 123, page 22, ibid., Vol. 180, page 18030 in a diffusion transfer process. In heat developable light-sensitive materials, however, they cause a reduction in the density of the image obtained because the bases are rapidly neutralized. Further, some compounds are known which release acids when heated. For example, in Japanese Patent Application (OPI) Nos. 58642/74 and 57452/75, there are disclosed acid components which at a temperature of at least 60.degree. C. are dissolved or release volatile acids. However, since the compounds disclosed in these patent applications neutralize the bases before development is started by heating, development is restrained and the density of the image obtained is reduced.